Polyacrylate-33 for Thickening and Suspending in Low Surfactant Cleansers

Aug 1, 2012 | Contact Author | By: Monique Adamy, Anne-France Leron, Charles Phan and Pascal Hervé, Rhodia
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Title: Polyacrylate-33 for Thickening and Suspending in Low Surfactant Cleansers
HASE polymersx surfactantx viscosityx yield stressx sulfate-freex
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Keywords: HASE polymers | surfactant | viscosity | yield stress | sulfate-free

Abstract: Described herein is a hydrophobically-modified acrylic copolymer, polyacrylate-33, which is designed for low-to-medium surfactant-containing cleansers. The ingredient is shown to display high thickening efficiency and good suspension properties and shear-thinning rheology in sulfate-based and sulfate-free chassis. Further, it enables transparent formulations in the presence of salt with improved foaming and sensorial properties.

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M Adamy, A-F Leron, C Phan and P Hervé, Polyacrylate-33 for thickening and suspending in low surfactant cleansers, Cosm & Toil 127(8) 574-583 (Aug 2012)

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Skin cleansing today has become a demanding, fragmented market that requires sophisticated products having a variety of appearances and textures. Clear formulas with suspended particles, beads or capsules, for aesthetic or functional benefits are more and more common. Mild cleansing products for sensitive skin are also a trend, and are usually based on sulfate-free formulas. Cleansers with added skin moisturizing and nourishing benefits, which often contain significant amounts of natural oils, are also growing areas, and as consumers expect such products to provide benefits beyond cleansing, the line between shower/bath products and skin care becomes blurred.

Beyond these trends, another focus for most product manufacturers is to lower the overall actives content in formulas—particularly in high-performance formulas, where lower surfactant levels are desired for economical and environmental reasons. The challenge for formulators is to achieve a significant reduction in the production cost while maintaining satisfactory performance for the consumer. This often involves incorporating performance additives in innovative, cost-effect ways to help compensate for the loss of certain attributes that necessarily follows from dilution.

Rheological solutions have continuously evolved to support these various needs. For conventional formulas, a number of commercial actives has been developed to impart viscosity, suspending power or both, based mainly on natural gums or synthetic polymers, which will be detailed later. However, to date, there is a clear gap between the available technological solutions and their successful application for specific textures, i.e., thickening, suspending and shear-thinning, without a negative impact on aesthetic benefits such as transparency; or performance attributes such as foam generation, cleansing and care.

The present article describes a hydrophobically-modified alkali swellable emulsion (HASE) polymer, polyacrylate-33, which was designed to close this gap. It abilities to solve formulating challenges especially in low-surfactant cleansing formulations, i.e., 6-13%, was assessed by viscosimeter and rheometer readings, UV/VIS spectrometer, foam readings and sensory testing.

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Table 1. Example formulations

Example formulations containing polyacrylate-33 and their properties

Figure 1. Schematic of an HASE particle in polyacrylate-33

Figure 1. Schematic of an HASE particle in polyacrylate-33

The good balance between thickening, shear-thinning rheology and suspension properties provided by polyacrylate-33 in surfactant solutions was obtained through the adequate selection of proprietary associative macro-monomers. Schematically, the structure of this HASE polymer resembles the schematic shown here.

Figure 2. Viscosity of the surfactant base 9/2% SLES/CAPB

Figure 2. Viscosity of the surfactant base 9/2% SLES/CAPB

Viscosity of the surfactant base 9/2% SLES/CAPB, at pH 6.5, as function of: a) increasing levels of rheological agent, in the absence of salt, and b) with increasing salt content, at a constant 2% active rheological agent. c) At 1% NaCl, the formulation with polyacrylate-33 was clear, while that with acrylated copolymer was turbid; note: Brookfield viscosity at 10 rpm.

Figure 3. Yield stress of formulas

Figure 3. Yield stress of formulas

Yield stress of formulas containing from 2.3–2.5% polyacrylate-33, with SLES/CAPB content varying from 7–13%; weight ratio SLES/CAPB = 4.5, at pH 6.5

Figure 4. Viscosity and transmittance responses

Figure 4. Viscosity and transmittance responses

Figure 4. Viscosity and transmittance responses, as a function of NaCl content, of an SLES9/CAPB2/Polyacrylate-331.5 / PQ-70.2wt% formula; pH = 6.5

Figure 5. Formulation characteristics, flow profiles and high throughput foam evaluations

Figure 5. Formulation characteristics, flow profiles and high throughput foam evaluations

Formulation characteristics, flow profiles and high throughput foam evaluations of three different formulas based on the same surfactant chassis but thickened with: a) 2.5% polyacrylate-33, b) 2.5% acrylates copolymer, and c) 3.3% acrylates copolymer; surfactant chassis composition, no added salt: SLES9/CAPB2wt% at pH 6.5

Figure 6. Handwash sensorial assessments

Figure 6. Handwash sensorial assessments

Handwash sensorial assessments averaged over 10 trained experts comparing polyacrylate-33 and acrylates copolymer in an SLES 5.6 /SLS3.4 / CAPB2.0wt% chassis at iso-viscosity (see text), Note: scale ranges from 1 (very low) to 5 (very high).

Footnotes [Adamy 127(8)]

a Rheomer 33 (INCI: Polyacrylate-33) is a product of Rhodia.

b The Brookfield Viscosimeter Model DV-I+ or DV-II+ was used at 10 RPM (spindle 4 or 5) for this study.

c The AR2000 Rheometer is manufactured by TA Instruments.

d The UV/VIS spectrometer Lambda Bio 40 is manufactured by PerkinElmer.

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